{"type_number":"GZ37","canonical_url":"https://tubeofile.com/tubes/GZ37","manufacturer":"Mullard","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"Octal","description":"Indirectly heated full-wave vacuum rectifier with a 5 volt heater. Designed for high-current power supply applications in audio amplifiers and industrial equipment. Higher current rating than the GZ34 but with a smaller maximum reservoir capacitor.","is_directly_heated":false,"completeness":"high","notes":["Maximum reservoir capacitor is only 4 µF (capacitor-input filter), much lower than the GZ34's 60 µF. This is a critical design constraint — most modern amplifier designs using large reservoir caps cannot use the GZ37 without modification.","Minimum series resistance per anode (Rftm) of 75 Ω is required for capacitor-input filter operation to limit peak charging current.","Choke-input filter operation allows significantly higher output current (350 mA vs 250 mA) and higher PIV rating (1850 V vs 1600 V).","Pin-compatible with 5U4G/5U4GB but the 5U4G is directly heated while the GZ37 is indirectly heated, giving the GZ37 a slower warm-up and reduced inrush stress on filter capacitors.","The CV378 made by GEC is designated U54 or 53KU; the Mullard-manufactured version is designated GZ37. Both meet the same CV378 military specification.","Pins 3, 5, and 7 are physically absent on the octal base (NP), not merely unconnected."],"references":["https://frank.pocnet.net/sheets/129/g/GZ37.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aaa1092.htm","tdsl":"http://tdsl.duncanamps.com/show.php?des=GZ37","radiomuseum":"https://www.radiomuseum.org/tubes/tube_gz37.html"},"raw_equivalents":["CV378","CV5745","53KU","U54","GZ34","5AR4"],"equivalents":[{"type_number":"GZ34","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"5U4G","reason":"Pin-compatible Octal pinout but directly heated vs indirectly heated — different warm-up and inrush characteristics","has_detail_page":true},{"type_number":"GZ33","reason":"Electrically similar but max reservoir capacitor is 60 µF vs 4 µF — different filter design constraints","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"4","function":"Anode 2","function_code":"a2","notes":null},{"pin_number":"6","function":"Anode 1","function_code":"a1","notes":null},{"pin_number":"8","function":"Heater / Cathode","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"5.0","numeric_value":"5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"2.8","numeric_value":"2.8","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Rectifier","tube_type_key":"rectifier","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"500","numeric_value":"500","unit":"V","param_group":"absolute_max"},{"key":"PIV","display_name":"Peak Inverse Voltage","value":"1600","numeric_value":"1600","unit":"V","param_group":"rectifier"},{"key":"Vdrop","display_name":"Voltage Drop (typical)","value":"30","numeric_value":"30","unit":"V","param_group":"rectifier"},{"key":"C_max","display_name":"Max C-input Filter Capacitor","value":"4","numeric_value":"4","unit":"µF","param_group":"rectifier"},{"key":"Ia_peak","display_name":"Peak Anode Current (surge)","value":"750","numeric_value":"750","unit":"mA","param_group":"rectifier"},{"key":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"250","numeric_value":"250","unit":"mA","param_group":"rectifier"},{"key":"Rs_min","display_name":"Min Series Resistance (C-input)","value":"75","numeric_value":"75","unit":"Ω","param_group":"rectifier"}]}],"synced_at":"2026-04-08T07:56:19.785Z"}